As described elsewhere, LEMIS takes a very hard stance against spammers. This can mean that you are affected if you use a webmail provider.
Once upon a time, large web services were also reputable and did their best to suppress spam. Things are changing, however: Yahoo!, once the webmail provider I recommended, has taken to spamming by itself. As a result, we have had no choice but to refuse all unidentified mail from Yahoo!.
If you are affected by this problem, and if you're not a spammer, you can get around this problem if you contact me. I will then add you to a whitelist which will enable you to contact me. If you're a spammer, this will also work. Once. After that, we will never have anything to do with you again.
See the "no spam" web page for more details. Below you can see the evidence of Yahoo!'s spamming, including the complete headers showing that this is not a spammer abusing Yahoo!s name, but Yahoo! themselves. They claim "opt-in", which is not correct, and which is a standard spam trick. I have never opted in for spam, neither with Yahoo!, nor with anybody else. As far as I know, I have no accounts of any kind at Yahoo!
First spam message
First spam complaint
Second spam message
Second spam complaint